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Hemodynamic Effects of Isoflurane in the Newborn Piglet

Comparison with Halothane

Received from the Departments of Anesthesiology/Critical Care Medicine and Pediatrics (Cardiology), Children's Hospital of Pittsburgh and the University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania.

Abstract

To better understand the mechanism of hypotension and bradycardia that may occur in newborn infants during isoflurane anesthesia, we studied the hemodynamic changes in the major determinants of cardiac output in 25 newborn piglets given 0.5, 1.0, and 1.3 minimal alveolar concentrations (MAC) of isoflurane and in nine sham-instrumented, age-matched control animals. Cardiac output did not differ from the baseline reading or the control group at any isoflurane dose. Mean aortic pressure (MAP) decreased 23–45% in a dose-related manner. Total peripheral resistance index (TPRI) decreased 29% at 0.5 MAC, but did not decline further at higher concentrations. Because the decrease in MAP was offset by a similar reduction in TPRI, cardiac output did not change. Heart rate decreased significantly at 1.3 MAC (–19%). Contractility was depressed at all concentrations: left ventricular dP/dT decreased progressively at 0.5 and 1.0 MAC, and echocardiographic shortening fraction decreased significantly at 1.0 MAC. Left ventricular end-diastolic pressure was not affected. Eight of twelve animals who had bradycardia while breathing isoflurane were atrially paced at their baseline heart rate. Because pacing did not restore MAP, TPRI, and LV dP/dT/DP40 (a contractile index independent of preload and afterload) to control values, bradycardia was not primarily responsible for depression of these variables. At equipotent concentrations, isoflurane reduced MAP and TPRI more than, and cardiac output less than, halothane did in previous studies in this laboratory. Heart rate and dP/dT were decreased to a similar extent by both agents. Blood, heart, and brainstem isoflurane LDMAC ratios were 2.04, 2.00, and 2.84, respectively, indicating a relatively low margin of safety for isoflurane in young piglets.

Key Words: ANESTHETICS, VOLATILE—isoflurane • HEART—myocardial function • ANESTHESIA—pediatric

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Anesthesia & Analgesia® is published for the International Anesthesia Research Society® by Lippincott Williams & Wilkins with the assistance of Stanford University Libraries' HighWire Press®. Copyright 2006 by the International Anesthesia Research Society. Online ISSN: 1526-7598   Print ISSN: 0003-2999